This invention concerns air balancing hoists of the type in which regulated air pressure is used to counter the weight of a suspended load to make it easier to maneuver the load by the hoist operator.
See U.S. Pat. No. 3,428,298 issued on Feb. 18, 1969 for a "Tool Balancer" for an example of such a hoist.
In this type of hoist, fluid pressure chamber is within the hoist housing acting on an axially movable piston, which in turn acts on a ball screw mechanism to cause a torque to be exerted on a cable drum to counteract the weight of a load suspended from a load cable wound on the drum.
An air pressure controller maintains a selectively set regulated pressure in the chamber so that if the load is pulled down, the resulting slightly increased pressure is relieved to allow lowering of the load to a new position. Alternatively, the pressure can be increased or decreased slightly to cause the load to be raised or lowered.
Sometimes bulky loads require additional hoists, with cables connected at spaced locations on the load. In this instance, special efforts must be taken to maintain the load in its desired initial horizontal orientation as it is raised or lowered by the above methods. Where the load weight is inadvertently shifted by tilting, this further complicates the problem as the balancing hoist will pay out or retract cable if the pulling force on its cable changes even slightly.
Accordingly, it is an object of the present invention to provide an arrangement for using two or more air balancing hoists for handling bulky load items which maintains a desired load attitude.